Magnesium chloride particles with a truncated structure, catalytic component supported on these particles, polyolefins obtained by employing this catalytic component, procedures for manufacturing these products

ABSTRACT

Porous particles of MgCl 2  which have essentially the shape of two truncated right cones connected by their larger bases, which truncated cones are incurved towards the axis of symmetry perpendicular to the bases, at the intersection of the envelope of the truncated cones with two orthogonal planes passing through the said axis of symmetry. These particles are impregnated with a transition metal compound and employed as a catalytic component in the polymerization of olefins. The resultant polyolefins, especially polyethylene, polypropylene and their copolymers, are comprised of particles with a distinctive structure.

BACKGROUND OF THE INVENTION

The present invention pertains to particles of magnesium chloride(MgCl₂) with a novel shape as well as to the procedure for manufacturingthese particles. These MgCl₂ particles can be employed as a catalyticsupport, especially in the catalytic components of the Ziegler-Nattatype. The polyolefins obtained by means of polymerization of olefins inthe presence of the catalytic component containing this MgCl₂ also havea distinctive structure. These catalytic components and the polyolefinsobtained in the presence of these components are also part of theinvention.

SUMMARY OF THE INVENTION

When viewed under a microscope, the MgCl₂ in accordance with theinvention is comprised of porous particles which have the shape of twotruncated right cones connected by their larger bases, which truncatedcones are incurved towards the axis of symmetry perpendicular to thebases, at the intersection of the envelope of the truncated cones withtwo orthogonal planes passing through the said axis of symmetry. The twotruncated cones are generally essentially identical and symmetrical andsuch that the ratio D:h of the largest diameter "D" of the bases to thetotal height "h" of the two connected truncated cones is between 1 and2, and more especially between 1.4 and 1.7. The usual D:d ratio of thelargest diameter "D" of the particle to the largest diameter "d" of thesmall base of the truncated cones is between 2 and 4, and moreespecially between 2.5 and 3.5. The invention also comprises catalyticcomponents embodying the MgCl₂ particles, polyoloefins obtainedutilizing such catalytic components, and the process of making suchproducts.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic side view of a MgCl₂ particle in accord with thepresent invention;

FIG. 2 is a top view taken along line 2--2 of FIG. 1;

FIG. 3 is a photomicrograph (1600×) of a MgCl₂ particle in accord withthe present invention;

FIG. 4 is a photomicrograph (200×) of a group of MgCl₂ particles inaccord with the present invention;

FIG. 5 is a photomicrograph (3000×) of a catalytic component particle inaccord with the present invention;

FIG. 6 is a photomicrograph (600×) enlargement of a group of catalyticcomponent particles in accord with the present invention;

FIG. 7 is a photomicrograph (20×) of a group of polyethylene particlesin accord with the present invention;

FIG. 8 is a photomicrograph (60×) of a group of polypropylene particlesin accord with the present invention;

FIG. 9 is a photomicrograph (20×) of a group of ethylene-1-butenecopoylmer particles in accord with the present invention; and

FIG. 10 is a photomicrograph (60×) of a group of propylene-ethylenecopolymer particles in accord with the present invention.

DETAILED DESCRIPTION

The four incurvations on each of the two truncated cones, separated fromeach other essentially by 90°, referring to FIGS. 1 and 2, can bedefined in relation to the largest radius "R" of the larger base of thetruncated cones and to the distance "E" separating the center of thislarger base of the truncated cone on this base from the point of maximumincurvation. This ratio R:E is generally between 1.1 and 1.5 and moreespecially between 1.2 and 1.4. These incurvations usually follow thetwo truncated cones from the larger base to the smaller base. Underthese conditions, the ratio r:e can be between 1.1 and 1.5 and moreespecially between 1.2 and 1.4, "r" being the largest radius of one ofthe two smaller bases of the truncated cones and "e" representing thedistance separating the center of this smaller base from the point ofmaximum incurvation on this same base.

These MgCl₂ particles have a rough and furrowed surface which assuresexcellent porosity. This porosity is generally between 0.5 and 3.5cm³/g, preferably between 1.5 and 2.5cm³ /g; it can be estimated that inthese particles the pores with radii between 5 and 100 nm represent upto 50% of the porous volume. Their specific surface area is usuallybetween 100 and 400m² /g, preferably between 200 and 300m² /g.

The size of the MgCl₂ particles is generally between 10 and 100μm,providing a narrow granulometric distribution. The D90:D10 range ofgranulometric distribution is usually lower than 4 and more generallylower than 3; D90 and D10 being the diameters smaller than which are 90%and 10% by weight of the particles, respectively.

These particles are obtained by precipitation with 1,4-dioxane of MgCl₂in solution in alcohol, with the said solution being emulsified in adispersant medium; the recovered MgCl₂ particles are then treated so asto totally eliminate the 1,4-dioxane.

The MgCl₂ to be treated is first put into solution in an alcohol underthe usual dissolution conditions at a concentration equal to at most thelimit of saturation at the temperature of the subsequent treatment ofthe solution. The alcohol employed is preferably a monoalcoholcontaining from 1 to 20 carbon atoms; n-butanol is the most highlyrecommended.

The solution of MgCl₂ in alcohol is emulsiifed in a dispersant medium,which is a liquid that is a nonsolvent of and inert in relation to thesolution, at a temperature than can range from room temperature to 100°C. Although it is not necessary, the emulsion can be prepared in thepresence of a surface-active agent, preferably a nonionic surface-activeagent. The liquid dispersant is preferably selected from among the heavyhydrocarbons with at least eight carbon atoms in their molecule, such asthe paraffin oils with a viscosity at 20° C. between 0.1 and 1 Pa.s. Inthe emulsion, the volume ratio of the dispersant medium to the alcoholphase, represented by the solution of MgCl₂ in alcohol, is usuallybetween 1 and 5, preferably between 2 and 4. As is known by the personskilled in this field, the agitation must be sufficient so as tomaintain the alcohol phase in the form of droplets in the dispersantmedium. As long as this condition is observed, the agitation conditionsdo not seem to be critical because, in particular, of a better stabilityof the emulsion at the procedure temperatures than at highertemperatures.

To this emulsion is added the precipitation agent which is 1,4-dioxane.The 1,4-dioxane is preferably added to the emulsion under agitation soas to assure immediate crystallization of the MgCl₂. The rate ofintroduction of the 1,4-dioxane does not appear to be critical; the1,4-dioxane may be added as quickly as possible or allowed to flowslowly into the emulsion. The temperature of the 1,4-dioxane at the timeof its introduction into the dispersion is also not critical. Incontrast, so as to assure excellent precipation of MgCl₂, it isrecommended that two volumes of 1,4-dioxane be employed per volume ofalcohol solution and to avoid allowing the temperature of the reactionmedium to drop below around 20° C.

The precipated MgCl₂ is in the form of particles as previously defined.This MgCl₂ is recovered in the form of a MgCl₂, 1,4-dioxane complexcontaining generally on the order of 67% by weight of dioxane and 33% byweight of MgCl₂. This complex must be treated so as to totally eliminatethe 1,4-dioxane from the MgCl₂. In fact, it is known that for certainapplications of MgCl₂, the presence of 1,4-dioxane is harmful,particularly when MgCl₂ is employed as a support for a Ziegler-typecatalytic component for polymerization; in fact, 1,4-dioxane has acatalyst-poisoning effect.

This dioxane can be eliminated from the MgCl₂ by any of the known meanssuch as heating under vacuum for a sufficient length of time such as,for example, at 200°-208° C. under a vacuum between 1 and 2 kPa, or byhot fluidization of the complex at, for example, 400° C. under an inertgas stream.

A particularly noteworthy means of eliminating the 1,4-dioxane from theMgCl₂ is comprised of treating the complex obtained with an aluminumcompound selected from among the nonhalogenated aluminoxanes, thenonhalogenated aluminosiloxanes or the AlR₃ alkylaluminums in which Rrepresents an alkyl radical containing from 1 to 20 carbon atoms. The1,4-dioxane removed from the MgCl₂ forms a complex with the aluminumcompound. In order to achieve this, the MgCl₂ 1,4-dioxane complex issuspended in an inert liquid which is a solvent of the aluminum compoundand the new complex formed: aluminum compound--1,4-dioxane afteraddition of the said aluminum complex. The inert liquid used forsuspending the MgCl₂ complex can be, for example, selected from amongthe saturated or unsaturated hydrocarbons such as hexane, heptane,benzene, toluene, the partially or completely chlorinated compounds witha larger dipole moment such as CH₂ Cl₂,C₂ H₄ Cl₂,CCl₄,C₂ Cl₄ ororthodichloro-benzene, or from among the aromatic compounds havinghydrocarbon groups and/or at least one chlorine atom. This treatmentwith the aluminum compound can be carried out under agitation at roomtemperature or under hot conditions, possibly under pressure so as toaccelerate the reaction. The treatment temperature is not critical; thistemperature is only limited by the boiling point of the inert liquidemployed as a suspension agent. It is recommended that in the suspensionan amount of aluminum compound be employed such that the molar ratioAl:1,4-dioxane be equal to or greater than 2. The excess of the aluminumis limited only by economic issues and the ease of washing. Rather thanemploying a large excess of the aluminum compound in the suspension, itis preferable for total elimination of the 1,4-dioxane to carry outmultiple treatments of the MgCl₂ with the aluminum compound. After theusual washings and rinsings for elimination of the final traces of thecomplex of the aluminum compound and 1,4-dioxane and possibly drying,the MgCl₂ recovered is essentially pure and contains more than 24% byweight of Mg; it also preserves the previously defined shape andcharacteristics.

When the MgCl₂ particles are intended for use as a transition-metalsupport of Ziegler-Natta type catalytic components, it can be of valueto not totally eliminate the aluminum compound which was used in thefinal treatment for eliminating the 1,4-dioxane.

X-ray observation of the MgCl₂ obtained shows a crystalline product withcertain diffraction peaks, including the peak located at circa0.181-0.184 nm (nanometer) that is characteristic of MgCl₂ as well asthree additional peaks located at circa 0.75-0.85 nm, 0.70-0.75 nm and0.50-0.52 nm. These measurements were carried out using PHILIPSequipment with the following characteristics:

scatter band of 1°

convergence aperture of 0.1°

nickel filter

normal focal tube made of copper

PW 1130 generator

PW 1050/25 goniometer

acceleration voltage=50 KV

emission intensity=30 mA

goniometer rotation rate: 1° (2 )/minute

By means of its novel structure, the MgCl₂ obtained has all of the sameadvantages as MgCl₂ with a spherical shape, while reducing itsdrawbacks. In order to obtain good pourability, as measured inaccordance with the standard ASTM D-1895, of the MgCl₂ and, moreparticularly, of the final polymer or copolymer, when the MgCl₂ isemployed as a catalytic support, research was focused on the particlestructures of MgCl₂. The spherical shape was particularly investigatedin the case of catalysis such that the final polymer or copolymerparticle, which essentially reproduces the support particle in ahomothetic manner, would have this pourability quality. The disadvantageof this sphericity is that it facilitates the accumulation ofelectrostatic charges in the reactors and conduits, thereby causing, inparticular, the adhesion of powder to the walls. The structure of theMgCl₂ in accordance with the invention makes it possible to reduce thistype of disadvantage.

A Ziegler-type catalytic component can be obtained by combining theMgCl₂ in accordance with the invention with a transition metal compound.Thus, for example, this type of component can be obtained by depositionon the MgCl₂ of a titanium and/or vanadium compound which is preferablyhalogenated and, more specifically, of TiCl₄, TiCl₃, VCl₄, VCl₃ orVOCl₃. This catalytic compound combined with a cocatalyst selected fromamong the organometallic compounds of metals I to III on the PeriodicTable and, more specifically, the aluminum compounds, is employed as acatalyst of the polymerization or copolymerication of linear or branchedolefins such as ethylene, propylene, 1-butene, 1-hexene, 1-octene,4-methyl-1-pentene, 1,3 butadiene and 1,9-decadiene.

At least one electron donor may be added during the preparation of thecatalytic component and/or the cocatalyst. The electron donors may beselected, for example, from among the Lewis acids, the esters ofoxygenated acids, the ketones, aldehydes, ethers, amines, amides, thesilicon compounds such as the silanes, and the phosphorus compounds suchas the phosphines and the phosphoramides; the preferred electron donorsbeing the alkylated esters or polyesters of aromatic acids, the alkylmono- or diethers, the alkoxysilanes and the alkylalkoxysilanes.

The catalyst obtained from a component prepared from the MgCl₂ of theinvention is suitable for all types of polymerization of olefins: athigh or low pressure, in suspension, in gas phase or masspolymerization.

The catalytic component obtained from the MgCl₂ in accordance with theinvention is also comprised of particles which, when viewed under amicroscope, have the shape essentially of two truncated right conesconnected by their larger bases, which truncated cones are incurvedtowards the axis of symmetry perpendicular to the bases, at theintersection of the envelope of the truncated cones with two orthogonalplanes passing through the said axis of symmetry. The two truncatedcones are generally essentially identical and symmetrical such that theratio D:H of the largest diameter "D" of the bases to the total height"h" of the two connected truncated cones is between 1 and 2 and, moreespecially, between 1.4 and 1.7. The usual ratio of the largest diameter"D" of the component particle to the largest diameter "d" of the smallbases of the truncated cones is between 2 and 4 and, more especially,between 2.5 and 3.5. The four incurvations on each of the two truncatedcones, separated from each other essentially by 90°, can be defined inrelation to the largest radius "R" of the larger base of the truncatedcones and to the distance "E" separating the center of this large baseof the truncated cones from the point of maximum incurvation on thissame base. This ratio R:E is generally between 1.1 and 1.5 and, moreespecially, between 1.2 and 1.4. These incurvations, which are much moreaccentuated at the large bases than at the small bases of the truncatedcones, usually follow each truncated cone from the larger base to thesmaller base. Under these condition, the ratio r:e can be between 1.1and 1.5 and, more especially, between 1.2 and 1.4, with "r" being thelargest radius of one of the two small bases of the truncated cones and"e" representing the distance separating the center of this small basefrom the point of maximum incurvation on this same base.

These catalytic component particles have an essentially smooth surface;the porosity of these particles is generally between 1 and 3 cm³ /g and,preferably, between 1.5 and 2.5 cm³ /g. Their specific surface area isusually between 100 and 400 m² /g and, preferably, between 200 and 300m² /g.

The size of the catalytic component particles is generally between 4 and100μm for a narrow granulometric distribution. The D90:D10 range ofgranulometric distribution, as previously defined, is usually lower than4 and more generally lower than 3.

The catalytic component can advantageously be prepared by impregnation,in a known manner, of the previously described MgCl₂ particles by atransition metal compound which is liquid or in solution and which hasone or more halogen atoms, particularly chlorine atoms. Prior to thisimpregnation or at least at the same time, it can be advisable to carryout the deposition of at least one organic compound selected from amongthe previously mentioned electron donors.

The resultant catalytic composition, combined with a conventionalcocatalyst, usually selected from among the organic aluminum compoundssuch as the aluminoxanes, the aluminosiloxanes, the compounds withAl-R-Al bonds in which R represents an alkyl group, or of formulaAlXqR's in which X represents Cl or OR' with R' designating a C₁ to C₁₆,preferably a C₁ to C₁₂, alkyl radical while q and s are numbers suchthat 1<s<3, 0<q<2 with q+s=3, form a catalyst which is suitable for thepolymerization of olefins and, more specifically, of ethylene,propylene, 1-butene, 4-methyl-1-pentene and 1-hexene or their mixtures.The possibility is not excluded of combining with the cocatalyst anelectron donor such as previously defined. The catalytic component andthe cocatalyst are combined in proportions such that the molar ratio ofthe aluminum contained in the cocatalyst to the transition metal of thesaid component is between 0.5 and 1000, preferably between 1 and 400.

The polymerization of the previously mentioned olefins or, in general,C₂ to C₁₂ olefins singly or in mixtures, by means of the previouslydefined catalytic system can be implemented in solution or in suspensionin an inert liquid medium and notably in an aliphatic hydrocarbon suchas n-heptane, n-hexane, isohexane, isobutane or mass polymerization canbe carried out in at least one of the olefins to be polymerized which ismaintained in the liquid or hypercritical state.

The operating conditions, notably the temperatures, pressures, amountsof catalytic system, for these liquid-phase polymerizations are thosewhich are usually recommended for the similar cases involving supportedor unsupported conventional catalytic systems of the Ziegler-Natta type.

For example, for polymerization carried out in suspension or in solutionin an inert liquid medium, one can operate at temperatures up to 250° C.and under pressures ranging from atmospheric pressure to 250 bar. In thecase of polymerization in a liquid propylene medium, the temperaturescan go as high as the critical temperature and the pressures can bebetween atmospheric pressure and the critical pressure. For masspolymerization or mass copolymerization of ethylene leading topolyethylenes or to a predominately ethylene-containing copoylmers, onecan operate at temperatures between 130° and 350° C. and a pressuresranding from 200 to 3500 bar.

The catalytic system obtained by combination of the transition metalcomponent according to the invention witha a cocatalyst and possibly anelectron donor as previously defined, can also be used for the gas-phasepolymerization of the previously mentioned olefins or olefins mixtures.Specifically, gas-phase polymerization can be carried out with contactof the said catalytic system with a mixture of ethylene or propylene andone or more C₂ to C₁₂ olefins such as ethylene, propylene, 1-butene,1-hexene, 4-methyl-1-pentene and 1-octene, which contains when it is incontact with the catalytic system a molar proportion of C₂ to C₁₂comonomers between 0.1 and 90%, preferably between 1 and 60%.

The gas-phase polymerization of the olefin or olefins in contact withthe catalytic system can be carried out in any reactor that allowsgas-phase polymerization, particularly in an agitated and/or fluided bedreactor. The implementation conditions for the gas-phase polymerizationnotably temperature, pressure, injection of the olefin or olefins intothe agitated and/or fluidized bed reactor, control of the polymerizationtemperature and pressure, are similar to those recommended in the priorart for the gas-phase polymerization of olefins. Operations aregenerally carried out at a temperature below the melting point Tf of thepolymer or copolymer to be synthesized, more specifically between +20°C. and (Tf -5)° C., and under a pressure such that the olefin orolefins, and possibly the other hydrocarbon monomers present in thereactor, are essentially in vapor phase.

The solution, suspension, mass, or gas-phase polymerization can becarried out in the presence of a chain-transfer agent so as to controlthe melt-flow index of the polymer or copolymer to be produced. Thepreferred chain-transfer agent is hydrogen which is used in an amountwhich can be as high as 90%, preferably between 0.1 and 60%, of thetotal volume of the olefins and hydrogen brought into the reactor.

The transition metal component in accordance with the invention can alsobe used for the preparation of an active prepolymer, which can be usedalone or in combination with a cocatalyst selected from the previouslydefined aluminum compounds.

The said active prepolymer is obtained by bringing into contact one ormore C₂ to C₁₂ alpha-olefins with a catalytic system formed by combiningthe transition metal component according to the invention with acocatalyst selected from among the compounds that were previouslymentioned for this purpose and employed in the previously specifiedproportions, with the said C₂ to C₁₂ olefin or olefins being used in anamount representing 2 to 500 grams, perferably 2 to 100 grams, of C₂ toC₁₂ olefin or olefins per gram of the transition metal component.

The catalytic component in accordance with the invention is particularlyvaluable in the polymerization or copolymerization of ethylene orpropylene or their mixtures with each other or with another olefin inthat it makes it possible to obtain polymers or copolymers with novelstructures to the extent, obviously, that the polymerization temperatureis lower than the melting point of the polymer formed.

When viewed under a microscope, the polyethylene or the copolymers ofethylene generally with more than 80% by weight of ethylene and at leastone other olefin, usually a C₃ to C₁₂ olefin, have the appearance ofparticles which are pierced centrally and comprised of a succession ofagglometrates attached to each other and arranged in a ring-like manner.These particles have an average size between 300 and 1000μm and arecomprised of agglomerates of a size generally between 50 and 400 μm,more specifically between 200 and 2000 μm. The polymer or copolymerobtained, which has a narrow granulometric distribution usually between3 and 4, has a high apparent density, measured according to the standardASTM D1895 Method A, benerally between 0.35 and 0.40 g/cm³. Thepourability of the powders is also high with values that are usuallylower than or equal to 20 seconds, according to the standard ASTM D1895.

When viewed under a microscope, the polypropylene or the copolymers ofpropylene and ethylene or at least one other C₄ to C₁₂ olefin, generallywith more than 80% by weight of propylene, have the form of particlescomprised of two truncated right cones connected by their larges bases,which truncated cones are incurved towards the axis of symmetryperpendicular to the bases, at the intersection of the envelope of thetruncated cones with two orthogonal planes passing through the said axisof symmetry. The two truncated cones are generally essentially identicaland symmetrical and such that the ratio D:h of the largest diameter "D"of the bases to the total height "h" of the two connected truncatedcones is between 1 and 2, more specifically between 1.4 and 1.7. Theusual ratio D:d of the largest diameter "D" of the particle to thelargest diameter "d" of the small bases of the truncated cones isbetween 2 and 4, more specifically between 2.5 and 3.5. The fourincurvations on each of the two truncated cones, separated from eachother essentially by 90%, can be defined in relation to the largestradius "R" of the larger base of the truncated cone and to the distance"E" separating the center of this larger base of the truncated conesfrom the point of maximum incurvation on this same base. This ratio R:Eis generally between 1.1 and 1.5, more specifically between 1.2 and 1.4.These incurvations usually follow the two truncated cones from thelarger base to the smaller base. Under these conditions, the ratio r:ecan be between 1.1 and 1.5, more specifically between 1.2 and 1.4, with"r" being the smallest radius of one of the two small bases of thetruncated cones and "e" representing the distance separating the centerof this small base from the point of maximum incurvation on this samebase. Attached FIGS. 1 and 2 show a front view and a top view of and arerepresentative of this polypropylene and its copolymers.

These propylene and propylene copolymer particles, the size of which isgenerally between 200 and 500 μm for a narrow granulometricdistribution, have a specific surface area between 0.1 and 3 m₂ /g. TheD90:D10 range of granulometric distribution is usually lower than 4,more generally lower than 3. The apparent densities of the propylenepolymers or copolymers are particularly high and generally between 0.45and 0.55 g/cm³. The pourability of the powders is usually between 20 and25 seconds.

The particles of polypropylene and its copolymers obtained from a MgCl₂component and/or support as previously described are generallyessentially homothetic to the particles of the MgCl₂ component and/orsupport.

The D90:D10 range of granulometric distribution is determined by meansof a MALVERN 1600 laser granulometer. The specific surface area ismeasured by isothermal physical absorption of nitrogen at thetemperature of liquid nitrogen, BET method, on a QUANTASORB device. Theporous volume is determined by intrusion of mercury under pressure withan ERBASCIENCE 1500 porosimeter.

The following examples illustrate the invention without, however,limiting it.

EXAMPLE 1

Into an agitated reactor thermostated at 40° C. and purged with drynitrogen are introduced 50 mL of a solution of MgCl₂ in n-butanol suchthat the BuOH:MgCl₂ molar ratio is 10. One then adds 200 mL of aparaffin oil with a viscosity of 0.2 Pa.s measured at 20° C. Agitationis brought to a speed such that the linear speed at the end of a bladeis 120 m/s. The biphasic mixture is left under agitation for 5 minutesand then 125 mL of 1,4-dioxane is added quickly and all at once.Precipitation of the MgCl₂, 1,4-dioxane complex is immediate. Afterfiltration, washing with hexane and drying under a nitrogen stream, onerecovers circa 14 g of a white pulverized powder with very goodpourability, the particles of which have a morphology corresponding toFIGS. 3 and 4. The composition of the solid prepared in this manner is67% 1,4-dioxane and 33% MgCl₂. The average largest diameter of theparticles is 27 μm and the D90:D10 ratio is 3.6. The specific surfacearea measured by BET is 4 m² /g and the porosity is 1.1 cm³ /g.

5.8 g of this composition is treated with a solution of triethylaluminumin 1,2-dichloroethane such that the Al:1,4-dioxane molar ratio is 2 andthe concentration in aluminum is 1 mole per liter. After filtration,washing and drying of the solid, one obtains a powder at least 80% ofthe structure of which corresponds to that in FIGS. 3 and 4. The meandiameter of the particles is 15 μm. The porosity is 2.16 cm³ /g for aspecific surface area of 272 m² /g, the mean D:h ratio=1.5 and the D:dratio=2.5 with R:E=1.2 and r:e=1.2. The D90:D10 ratio=3.5. The MgCl₂contains 24.5% Mg.

This powder is taken up in 50 mL of a solution of dioctyl phthalate in1,2-dichloroethane at 0.2 mole for 2 hours at 80° C. After filtration,50 mL of pure TiCl₄ is added to the MgCl₂. After 2 hours under agitationat 80° C., a new filtration is carried out and the solid is taken up in50 mL of a solution of 1,2-dichloroethane containing 1 mole of TiCl₄ for30 minutes at 80° C. under agitation. After filtration, this treatmentwith dilute TiCl₄ is carried out again. After filtration, washing withhexane and drying, one obtains 1.9g of catalytic component containing69%, 23.8% and 0.9% by weight of chlorine, magnesium and titanium,respectively. The structure of the component particles obtainedcorresponds to those of FIGS. 5 and 6. The mean diameter of theparticles is 15 μm and the range of the granulometric distribution is3.4. On average, the particles have the following characteristics:D:h=1.5, D:d=2.5, R:E=1.2 and r:e=1.2. Their mean porosity is 2.2 cm³ /gfor a specific surface area of 290 m² /g.

Into a stainless steel reactor are introduced 1.2 L of hydrogen, 600 gof liquid propylene, 1.3 g of triethylaluminum and 0.1 molar equivalentin relation to the aluminum of cyclohexylmethyldimethoxysilane. 20 mg ofthe prior catalytic component is added. The reactor is kept underagitation for 1 hour at 70° C.

One recovers 172 g of polypropylene with good pourability, the structureof the particles of which corresponds to that shown in FIG. 8. The meandiameter of the polymer particles is 270 μm and the range ofgranulometric distribution is 2.6. The level of fine particles smallerthan 10 μm is 0.2 %. The apparent density is 0.46 g/cm³ and thepourability is 21 seconds. The level of polymer insoluble in boilingheptane is 95.1%. The melt-flow index measured according to the standardASTM D1238 Method L is 4.

EXAMPLE 2

A MgCl₂ powder is prepared under the conditions of Example 1 except thatthe operation is carried out at 65° C. rather than 40° C. 14 g of powderis finally obtained and treated with a solution of triethylaluminum in1,2-dichloroethane under the same conditions as in Example 1. The finalstructure of the particles corresponds to that shown in FIGS. 3 and 4.The mean diameter of the particles is 35 m and the range of theirgranulometric distribution is 3.8. The porosity=1.7 cm³ /g, the specificsurface area=229 m² /g, D:h=1.6, D:d=3, R:E=1.3, r:e=1.3, Mg =24.3%. Thepowder obtained is put into suspension in 50 mL of pure TiCl₄ for 3hours at 80° C. After filtration, washing with hexane and drying, thecatalytic component obtained contains 23.5%, 1.4% and 71.3% by weight ofmagnesium, titanium and chlorine, respectively. The structure of theparticles of the resultant component corresponds to that of FIGS. 5 and6. The mean diameter of the particles is 30 μm and the range of thegranulometric distribution is 3.3. On average the particles have thefollowing characteristics: D:h=1.6, D:d=3, R:E=1.3, and r:e=1.3. Theirmean porosity is 1.53 cm³ /g for a specific surface area of 207 m² /g.

Into a stainless steel reactor, one introduces under nitrogen 2 litersof hexane, 10 mM of triisobutylaluminum and 10 mg of the precedingcatalytic component. The temperature is brought to 86° C. The reactionmedium is put under a pressure of 0.4 MPa of hydrogen. The reactor isfed with a mixture of ethylene and of 1-butene at 1% 1-butene. Themonomer pressure is 0.6 MPa. After three hours of reaction, one recovers173 g of ethylene-butene copolymer with very good pourability, thestructure of the particles of which corresponds to that shown in FIG. 9.The mean diameter of the polymer particles is 500 μm and the range ofgranulometric distribution is 3.8. The apparent density is 0.35 g/cm³and the pourability is 19 seconds. The melt-flow indices measuredaccording to the standard ASTM D1238 Methods E and F are 1 and 34,respectively.

EXAMPLE 3

With all other conditions corresponding to those of Example 1, 240 mL ofbutanol solution of MgCl₂ and 1150 mL of paraffin oil are employed. Thelinear agitation speed at the end of the blade is 280 m/s and theoperating temperature is 90° C. 700 mL of 1,4-dioxane is added. Oneobtains 66 g of powder, the structure of the particles of whichcorrespons to that shown in FIGS. 3 and 4. The mean diameter of theparticles is 15 μm and the range of granulometric distribution is 3.5.The porosity=2.1 Cm³ /g, the specific surface area=217 m² /g, D:h=1.5,D:d=3, R:E=1.2 and r:e=1.2

EXAMPLE 4

Use is again made of the catalytic component as described in Example 2.

The homopolymerization of ethylene is carried out under the sameconditions as those of Example 2, except with regard to the partialpressures of hydrogen and ethylene which are 0.47 MPa and 0.63 MPa,respectively. After 2 hours of reaction, 53 g of polyethylene arerecovered. The structure of the particles corresponds to that shown inFIG. 7.

The mean diameter is 640 microns. The range of granulometricdistribution is 3.4. The apparent density is 0.37 g/cm³ and thepourability is 20 seconds.

The melt-flow indices measured according to the standard ASTM D1238Methods E and F are 3.5 and 108, respectively.

EXAMPLE 5

The catalytic component described in Example 1 is employed in thecopolymerization of propylene and ethylene. Into a stainless steelreactor purged with nitrogen are introduced in order: 1.2 liters ofhydrogen, 600 g of liquid propylene, 1.3 g of triethylaluminum and 0.1molar equivalent in relation to the aluminum ofcyclohexylmethyldimethoxysilane. Twenty mg of the catalytic component isthen added and the temperature is raised to 70° C.

As soon as the reaction temperature reaches 70° C., ethylene at a flowrate of 10 Nl/min is introduced into the reactor for 1 hour.

After degassing the reactor, 160 g of propyleneethylene copolymer isrecovered.

The structure of the particles corresponds to that of FIG. 10. The meandiameter is 330 μm and the range of granulometric distribution is 3.6.The level of fine particles smaller than 100 μm is 1%.

The apparent density is 0.43 g/cm³ and the pourability is 25 seconds.

The melt-flow index of the copolymer measured according to the standardASTM D1238 Method L is 2.5. The level of copolymer insoluble in boilingheptane is 82%. Infrared analysis of the level of ethylene in thecopolymer yielded a value of 3.5 % by weight.

While the invention has been described in connection with a preferredembodiment, it is not intended to limit the scope of the invention tothe particular form set forth, but on the contrary, it is intended tocover such alternatives, modifications, and equivalents as may beincluded with the spirit of the invention as defined by the appendedclaims.

What is claimed is:
 1. Porous particles of MgCl₂ having the shapeessentially of two truncated right cones connected by their largerbases, which truncated cones are incurved towards the axis of symmetryperpendicular to the bases, at the intersection of the envelope of thetruncated cones with two orthogonal planes passing through the said axisof symmetry.
 2. The particles of MgCl₂ of claim 1, wherein the twotruncated cones are essentially identical and symmetrical.
 3. Theparticles of MgCl₂ of claim 2, wherein the ratio D:h of the largestdiameter "D" of the bases to the total height "h" of the two connectedtruncated cones is between 1 and
 2. 4. The particles of MgCl₂ of claim3, wherein the ratio D:d of the largest diameter "D" of the particle tothe largest diameter "d" of the small bases of the truncated cones isbetween 2 and
 4. 5. The particles of MgCl₂ of claim 4, wherein the fourincurvations are separated from each other essentially by 90°.
 6. Theparticles of MgCl₂ of claim 5, wherein the ratio R:E of the largestradius "R" of the larger base of the truncated cones to the distance "E"separating the center of this larger base from the point of maximumincurvation on this same base is between 1.1 and 1.5.
 7. The particlesof MgCl₂ of claim 6, wherein the ratio r:e of the largest radius "r" ofthe two small bases of the truncated cones to the distance "e"separating the center of this small base from the point of maximumincurvation on this same base is between 1.1 and 1.5.
 8. The particlesof MgCl₂ of claim 7, wherein their porosity is between 1.5 and 2.5 cm³/g.
 9. The particles of MgCl₂ of claim 8, wherein their specific surfacearea is between 100 and 400m² /g.
 10. The particles of MgCl₂ of claim 9,wherein the size of the particles is between 10 and 100 μm with aD90:D10 range of granulometric distribution lower than
 4. 11. Theparticles of MgCl₂ of claim 10, wherein under X-ray analysis, inaddition to the characteristic diffraction peak of MgCl₂ located atcirca 0.181-0.184 nm, there are three peaks located at circa 0.75-0.85nm, 0.70-0.75 nm and 0.50-0.52 nm.
 12. The process for the preparationof the MgCl₂ having the shape essentially of two truncated right conesconnected by their larger bases, which truncated cones are incurvedtowards the axis of symmetry, perpendicular to the bases, at theintersection of the envelope of the truncated cones with two orthogonalplanes passing through the said axis of symmetry comprising dissolvingMgCl₂ in an alcohol, emulsifying the alcohol solution in a liquiddispersant which is a nonsolvent and inert in relation to the solutionand precipitating the MgCl₂ in the form of a MgCl₂ -1,4-dioxane complexby addition to the emulsion of 1,4-dioxane.
 13. The process of claim 12,wherein the alcohol is selected from among the monoalcohols containingfrom 1 to 20 carbon atoms.
 14. The process of claim 13, wherein theliquid dispersant is selected from among the hydrocarbons with at least8 carbon atoms.
 15. The process of claim 14, wherein the liquiddispersant is a paraffin oil with a viscosity between about 0.1 and 1Pa.s at 20° C.
 16. The process of claim 15, wherein the ratio of theliquid dispersant to the alcohol solution is between 1 and
 5. 17. Theprocess of claim 16, wherein at least two volumes of 1,4-dioxane pervolume of alcohol solution are used for precipitation.
 18. The processof claim 17, wherein the 1,4-dioxane is eliminated from the MgCl₂-1,4-dioxane complex.
 19. The process of claim 18, wherein the1,4-dioxane is eliminated by heating under a vacuum.
 20. The process ofclaim 18, wherein the MgCl₂ -1,4-dioxane complex is treated with analuminum compound selected from among the nonhalogenated aluminoxanes,the nonhalogenated aluminosiloxanes or from among the alkylaluminums,AlR₃ in which R₃ represents alkyl radical containing between 1 and 20carbon atoms.
 21. The process of claim 20, wherein the Al:1,4-dioxanemolar ratio is equal to or greater than
 2. 22. A catalytic componentcomprising MgCl₂ particles impregnated with a transition metal compound,said particles having essentially the shape of two truncated right conesconnected by their larger bases, which truncated cones are incurvedtowards the axis of symmetry perpendicular to the bases, at theintersection of the envelope of the truncated cones with two orthogonalplanes passing through the said axis of symmetry.
 23. The catalyticcomponent of claim 22, wherein the two truncated cones of each particleare essentially identical and symmetrical.
 24. The catalytic componentof claim 23, characterized in that in the particles the ratio D:h of thelargest diameter "D" of the bases to the total height "h" of the twoconnected truncated cones is between 1 and
 2. 25. The catalyticcomponent of claim 24, wherein in the particles the ratio D:d of thelargest diameter "D" of the component particle to the largest diameter"d" of the small bases of the truncated cones is between 2 and
 4. 26.The catalytic component of claim 25, wherein in the particles the fourincurvations are separated from each other essentially by 90°.
 27. Thecatalytic component of claims 26, wherein in the particles the ratio R:Eof the largest radius "R" of the larger base of the truncated cones tothe distance "E" separating the center of this larger base from thepoint of maximum incurvation on this same base is between 1.1 and 1.5.28. The catalytic component of claim 27, wherein in the particles theratio r:e of the largest radius of one of the two small bases of thetruncated bases to the distance "e" separating the center of this smallbase from the point of maximum incurvation on this same base is between1.1 and 1.5.
 29. The catalytic component of claim 28, wherein theporosity of these particles is between 1 and 3 cm³ /g.
 30. The catalyticcomponent of claim 29, where its specific surface area is between 100and 400 m² /g.
 31. The catalytic component of claim 30, wherein the sizeof its particles is between 5 and 100 μm with a D90:D10 range ofgranulometric distribution smaller than
 4. 32. The catalytic componentof claim 30, wherein it is obtained by impregnation with a halogenatedtitanium compound.